The present invention generally relates to fluid filters, and more specifically, but not exclusively, concerns a fluid filter with a compact design that minimizes fluid flow restrictions.
While the design of fluid filters over the years has involved literally hundreds of different concepts, the basic principles of operation have remained much the same. A fluid substance to be filtered must first be introduced into a filter housing or shell, and from there, the fluid is directed to flow into and through a filtering media. As the fluid exits from the filtering media, fluid is routed to a flow outlet. Throughout this flow loop, it is generally preferred that the unfiltered fluid not bypass the filtering media and that the fluid not leak from the filter shell. While these functions can normally be achieved by the use of properly designed and positioned seals, over time the seals deteriorate and leakage can occur. The passage of time and continuous use can also cause deterioration of other components and interfaces within the fluid filter.
For example, each pulse of fluid pressure creates a variable load on the nutplate of the fluid filter causing the nutplate to flex. The flexing of the nutplate creates wear on the plate and weakens the nutplate interfaces. In particular, this flexing causes the outer seal to deflect which can in turn create a leakage interface. To some extent, the rate of deterioration is affected by the operating environment and the nature of the substance being filtered. If a longer service interval is desired for the filter assembly, it is important to be able to slow the rate of deterioration.
Another source of leakage comes from vibration of the nutplate. Vibrations due to engine operation and those coming from road conditions are transmitted to the fluid filter assembly by the filter-mounting base of the engine. The distance from the outside diameter of the stem to the filter housing (i.e., shell) defines the moment arm about which the filter assembly is able to move. The greater length the moment arm, the greater amplitude of the transmitted vibrations and the greater rate of deterioration of the seals of the fluid filter assembly. This in turn increases the rate of deterioration of the filter assembly. Vibrations of the type described above also have a deterioration effect upon the seals, the nutplate, and other structure components of the fluid filter.
One solution to this problem is to increase the size of internally threaded aperture in the nutplate. However, this solution creates new problems related to formation of fluid flow apertures. With traditional nutplates, there is a significant area on the radius bend portion for fluid inlet apertures to be molded, cast, or machined directly into and through the nutplate. In contrast, the nutplate with the larger internally threaded portion has a smaller land area on the bend portion. This means that any flow hole which would be drilled, cast, or molded through that area must be extremely small. In order to generate adequate fluid flow, a large number of these holes would be required to create a sufficient flow area. This would substantially weaken the nutplate.
One solution to this flow aperture problem has been to use a specially designed inner seal. This specially designed inner seal has standoffs that maintain flow openings between the nutplate and the filter element. Instead of flowing through holes in the nutplate, the fluid flows through the openings maintained by the standoffs. With another design, the openings are maintained by standoffs that are formed on the nutplate. Forming the standoffs on the nutplate makes the shape of the nutplate more complicated, which in turn increases manufacturing costs and reduces the overall strength of the nutplate. In this design, the inner seal is also specially designed to ensure that the inner seal is properly secured within the filter.
However, these specially designed inner seals create a whole host of new problems. One problem is that these specially designed inner seals have complicated shapes, which make manufacturing of the seals expensive. Other problems are experienced during the installation and servicing of the filter. The structure of the filter does not allow for self-centering of the filter element, which can make installation of off-centered filter elements difficult. Since the specially designed inner seals are elastic, the seals are susceptible to twisting during servicing or assembly. Further, the elastic (rubber) standoffs on the inner seals can compress so as to restrict fluid flow. In order to compensate for this standoff compression, the elastic standoffs are designed with a larger uncompressed profile, and this in turn unnecessarily increases the overall size of the filter. During operation, space is limited to accommodate swelling of the specially designed inner seal, and this can lead to over compression of the inner seal against the filter head. A large amount of force then has to be applied in order to break the filter loose from the filter head. While important strides have been made in this field, there is still room for improvements in the areas of fluid control and installation/removal of fluid filter assemblies.
A fluid filter includes a filter element, a nutplate, an inner seal retainer, and an inner radial seal. The nutplate has a threaded mounting portion, and the nutplate is adapted to threadedly engage an externally threaded filter head. The inner seal retainer is positioned between the nutplate and the filter element. The inner seal retainer has at least one standoff that is adapted to provide a space for transmitting fluid between the nutplate and the filter element. The inner radial seal is coupled to the inner seal retainer in order to seal the filter element with the filter head.